248 
=—26 
-28 
ae 
-120 aC -100 -90 
Poison temperature, °C 
Cloud temperoture 
A ed 
i) ° 
1 
ao 
- 
Fic. 1—Inhibition of lead iodide nucleation of 
supercooled water by ethyl amine 
SEYMOUR BIRSTEIN 
Fig. 2—Nuclei generator 
Fic. 3—Cross section of the eryostat 
The cold box used in these experiments (Fig. 
4) was of conventional design and it, too, was 
designed in this laboratory [Birstein, 1954]. It 
consisted of a dewar flask L filled with methanol 
in which was suspended a brass cylinder M closed 
on one end and covered on the other with a 
removable plexiglas lid. Ice crystal formation 
was monitored by shining a beam of parallel 
light through the transparent top. The chamber 
N 
ries 4— Cold box 
was cooled by circulating refrigerated methanol 
through a copper coil immersed in the dewar. 
The temperature of the cold box J and K, too, 
was controlled by means of a Tag controller- 
indicator T whose thermocouple was suspended 
in the cold box to sense the temperature and, 
therefore, control the flow of refrigerant through 
the valve D. 
Discussion—From Figure 1, it can be seen that 
even in a dynamic system the effect of ethyl 
amine on lead iodide nucleation of supercooled 
water is quite marked. A comparison of the data 
from the dynamic system with those obtained 
from the static tests under known equilibrium 
conditions shows that there is, in general, good 
agreement between the two sets of data. While 
the static tests were quite interesting, because of 
the nature of the apparatus used, it was only 
possible to run the tests at relatively high partial 
pressures of ethyl amine. The system used in- 
volved the passing of a nitrogen stream contain- 
ing the nuclei over a saturator filled with the 
amine. The lowest temperature which could be 
reached in the saturator was approximately 
—110°. At —105° the vapor pressure of the ethyl 
amine is on the order of 0.1 mm or approxi- 
mately 0.0001 atmosphere. With the cryostat 
used in the static measurements, it was possible 
to reach a temperature approaching the boiling 
point of the coolant. In the case of liquid nitro- 
gen which boils at —196°, the cryostat tempera- 
ture could be lowered to approximately —180°. 
The vapor pressure curve for ethyl amine is 
shown in Figure 5. The curve for the plot of log 
vapor pressure as a function of temperature can, 
for all practical purposes, be assumed a straight 
line in this range. The results of the static runs 
are given in Table 1. The cryostat temperature 
ethyl amine vapor pressure, and nucleation 
